At the end of “The Disaster Artist,” the novice filmmaker Tommy Wiseau puts on a tuxedo and attends the premiere of his new movie, which he believes is a masterpiece as profound as anything in cinematic history. (He is its director, producer, screenwriter and star.) Unfortunately, the film, “The Room,” is a flat-out awful compendium of excruciating dialogue, incoherent plot twists and strangely wooden yet melodramatic acting.

The audience is puzzled, then horrified, then delighted, and right before our eyes Tommy (James Franco) has to perform a tricky bit of emotional jujitsu, jettisoning his delusions and accepting that if the public loves his film, it’s only because it is so terrible. That’s the subtext of “The Disaster Artist,” due Dec. 1, a based-on-a-true-story movie that also explores friendship, obsession, Hollywood and the rich comedic possibilities of the line “You’re tearing me apart, Lisa!”

How do you handle it when the movie that you meant to be one thing turns out to be a different thing entirely?

“The Room” was made for something like $6 million of Mr. Wiseau’s nebulously obtained fortune. It opened in 2003, in a theater in Los Angeles that he had to rent himself, and made $1,800 its first weekend. But word spread that it was a camp classic — an amalgamation of absurd non sequiturs, continuity problems and characters of dubious motivation who come and go for no particular reason, in the service of a story involving a cheating girlfriend, a betrayed friendship and a lot of scenes of guys tossing around footballs. Now it plays to packed, “Rocky Horror”-style interactive audiences around the world and appears to have made back its investment.

Best of The RoomCreditVideo by Conner Wiltshire

Video

A preview of the filmPublished OnNov. 27, 2017CreditImage by Internet Video Archive

At its center is the slight, longhaired, sunglasses-sporting, black-clad Mr. Wiseau, who has spent the intervening years doing two things: promoting the film, and maintaining the carefully constructed aura of mystery that swirls around him as thickly as if it were generated by a Hollywood fog machine.

Despite being the subject of the new movie as well as the 2013 book on which it is based (also called “The Disaster Artist” and written by Greg Sestero, Mr. Wiseau’s “Room” co-star and weirdly codependent friend, along with Tom Bissell), Mr. Wiseau remains a cipher wrapped in an enigma packaged in a carapace that recalls Keith Richards attending a vampire-themed Halloween party.

“People don’t understand me as a person,” Mr. Wiseau said, speaking by phone from Hollywood. He sounds exactly the way Mr. Franco does in the film, with idiosyncratically mangled syntax and a sui generis accent that is vaguely Eastern European, but that he refers to as Cajun.

In “The Disaster Artist,” Tommy indignantly refuses to tell Greg (played by Mr. Franco’s younger brother Dave) anything personal about himself, including his age, how he made his money, or why he insists he is from New Orleans when he is so obviously from someplace else. Asked these same questions now for journalistic purposes, Mr. Wiseau remains slightly less vague, but just as irritable.

“It’s not important, and No. 2, it’s a personal question,” he said. “Long story short, I grew up in Europe a long time ago, but I’m American and very proud of it. Do you have any questions about the movie?”

For years journalists have tried to pin down these specifics, with what appears to be some success; IMDB.com now simply says he was born in Poland in 1955. As for his fortune, he said it came from his leather-jacket and real-estate businesses.

The Tommy of “The Disaster Artist” seems just shy of being certifiably crazy. He’s erratic and demanding and grandiose and insecure, all at once. Greg serves as his non-insane foil, remaining relatively normal despite what appears to be his poor judgment in assisting and starring in his friend’s film.

It’s hard to understand what drew them together, but, the real Mr. Sestero said, Mr. Wiseau gave him a way to fulfill his dream of becoming a Hollywood star. “I was very much taken with Tommy when I first met him,” he said by phone from Los Angeles. “He represented freedom to me. He was the answer to so many questions I had. I looked up to him and needed him, and that kind of went both ways.”

The people involved in the new movie, including James Franco, who directed as well as starred in it, and Seth Rogen, who plays a seasoned script supervisor who clashes with Tommy on the set, have their own fascinations with Mr. Wiseau. Mr. Rogen, who is also a producer of “The Disaster Artist,” has been a fan of “The Room” for years, since the actor Paul Rudd took him to see it.

“We became obsessed with it,” he said in a telephone interview. “It is particularly fascinating to comedy people. Most movies that are this catastrophically bad are in a genre that contributes to their failure — like a science-fiction film that didn’t have the budget for what they were trying to do — but this is a character drama that’s really personal. The fact that this guy made all these choices was so strange.”

Image

Filmmakers in conversation: Mr. Wiseau with Mr. Franco in Los Angeles in November.CreditJake Michaels for The New York Times

Mr. Rogen and Mr. Franco both put the $64,000 question to Mr. Wiseau: Given how wedded you were to the serious nature of your film, how do you feel about the fact that everyone else finds it so funny?

“It takes an incredibly savvy person to answer it in the way he does,” Mr. Rogen said, “which is to validate that people like it in a different way, but talk about it as if they are reacting in exactly the way he intended. It’s a semantical slalom that he navigates extremely well.”

Mr. Franco, who won best actor at the Gotham Awards, kicking off Oscar season, added by phone: “Whatever happened to Tommy, there’s something he needed to prove or fill, and he got that from ‘The Room.’”

He continued: “Now we’re in the third phase of the Tommy saga. Pre- ‘Room’ he felt he couldn’t depend on anybody, and the film was him trying to wrestle with feelings of rejection he’d had his whole life. And then it came out and he thought he had to maintain this persona of Tommy, and pretend that he had intended it to be comedy. And now there’s this new phase where people are getting to see the other side of him.”

“When the movie was shown at South by Southwest, they were cheering on his story,” Mr. Franco went on. “I realized later that it was probably the first time that Tommy heard unironic applause, just for him.”

What does Mr. Wiseau say, when you ask him directly?

“To respond to your question without avoiding it, I didn’t realize, to be honest, that I’d created something that people would interact with in this way,” he said. “But you as an actor cannot criticize the audience, and the audience is having fun.” He added: “If you have a drama, you can find a comedy. If you have a comedy, you can find the drama.”

Though he is pleased about the new movie, he takes issue with Mr. Sestero’s account of him as tyrannical and cruel on the “Room” set.

“The movie was produced in a very respectful way based on formula I studied as a producer, actor and director,” he said. “You can look at it two ways. You analyze Marlon Brando, you analyze James Franco, you analyze James Dean, you analyze Tommy Wiseau and I hope you come to the same conclusion: We are good actors. But you are here to please your audience, not yourself, that’s No. 1.”

Referring to his detractors, he went on: “I have advice for all of you bad apples. Be nice. Grab the camera and roll the movie and see what happens. Before you start criticizing anybody, see how hard it is to make a movie.”

Here’s something curious: Mr. Wiseau and Mr. Sestero are still incredibly close. Mr. Sestero, whose last serious romantic relationship foundered on the set of “The Room,” has spent the last few years publicizing his book and doing “Room”-related projects.

The makers of “The Disaster Artist” originally ended the film with the dissolution of Tommy and Greg’s friendship — a reasonable assumption, based on Mr. Sestero’s book.

“But then I watched Greg talk to Tommy on the phone for an hour every day,” Mr. Rogen said. “I was thinking, ‘That’s not the story.’ And we changed the film because of their actual relationship.”

Mr. Sestero has a new film due in 2018 that stars Mr. Wiseau as a strange mortician and himself as the strange-in-a-different-way homeless man who together embark on various crime and cadaver-related escapades. It is called “Best F(r)iends.”

Correction:

An earlier version of this article omitted the co-author of the book “The Disaster Artist.” Tom Bissell wrote it along with the actor Greg Sestero.